It is too early to tell, however, whether the microblogging
website will adopt the kind of financial structures favoured by
other internet firms such as Google,
Amazon and eBay to
lower their UK tax bills.

Very little is known about the finances of the San
Francisco-based group, which is incorporated in the US tax and
secrecy haven of Delaware. The business is estimated to have
taken $288m in global advertising revenues last year, according
to the research firm eMarketer – a figure that is projected to
rise to $545m this year and $807m by 2014.

While the US only accounts for 10% to 20% of Twitter's estimated
200 million active users around the world, eMarketer researchers
estimate the more commercially mature US market will still
generate 83% of the group's advertising revenues for 2013.

So-called "promoted" adverts started appearing on Twitter feeds
in 2010 in the US, and in Britain in
September the following year. Among the first advertisers
targeting the UK that autumn were Sky, BT, Eurostar, Electronic
Games and Paramount Pictures UK.

By 2011, just $5.6m, or 4%, of the group's ad revenues were
estimated to have come from markets beyond the US. The UK was one
of the first new territories targeted, with a small staff
recruited in central London in May 2011 about the same time as
the firm acquired the filtering site Tweetdeck, located near
London's so-called "Silicon Roundabout".

Abbreviated accounts, covering the first seven months of Twitter
UK's life, were only signed off by Ali Rowghani, the US group's
chief financial officer, last month. The three-person board
consists of Rowghani, Twitter chief executive Dick Costolo and
the site's group counsel Alex MacGillivray – all of whom are
based in San Francisco. The UK firm's registered office is given
as that of its solicitors, Baker & McKenzie.

Small British firms can file abbreviated accounts if they meet
two of three conditions: having turnover less than £6.5m, a
balance sheet under £3.26m, and with fewer than 50 staff.

Twitter UK's parent company is a holding company in Ireland
called Twitter International Company. The Irish firm is not
required to file accounts and is ultimately owned by the
Delaware-incorporated Twitter Inc.

Last month Google's boss, Eric
Schmidt, brushed aside criticisms of the group's elaborate
corporate structure – involving an international company in
Ireland and a parent company Delaware – which have seen it shift
revenues of about $9.8bn into a Bermuda shell company where they
are sheltered from tax. "It's called capitalism. We are proudly
capitalistic. I'm not confused about this."

A Twitter spokesperson declined to comment on the record but
privately insisted that figures in the 2011 accounts for its
British subsidiary were in line with the scale of UK trading at
that time.